This invention relates to electrical transformers of a type in which the primary and secondary portions are separable. More particularly, it relates to an inductor than can be embedded in a plastic credit card to receive magnetically transmitted power and information.
The use of plastic credit cards for credit purchases and for banking transactions has become so popular that most travelers today do so with very little cash. The card, embossed with an account number and the name of the account owner, serves solely to identify an authorized account to be charged for the transaction. A magnetic strip on the back of some cards contains the same information but is machine readable to speed the transaction. All accounting information is stored at the bank or credit house.
As a result, it is easy for a thief to use a stolen card or for a legitimate owner to exceed his credit limit. Most merchants, therefore, require that before purchases above a relatively modest amount such as $50 are completed, the authorization must be verified with the credit house. Even with automatic telephone dialing the procedure is cumbersome and time consuming. Furthermore, a separate card is needed for each account. With the advent of recent advances in microcircuitry, however, it is now possible to put a vast amount of computing power and memory right in the card to produce a "smart card" or "personal card." The card could therefore carry personal identification data to virtually eliminate fraudulent use--such data as personal characteristics, driver's license and Social Security numbers, personal key numbers and even voice prints. The card could also carry the account numbers of all of the owners' charge accounts, the balances of all of the accounts, the credit limits of all of the accounts, and other such personal data as, for example, the sizes of family members for clothing purchases, personal telephone directories, etc. The types of personal data are limited only by one's imagination.
The technology for putting all of this on the standard size plastic card is here. What is holding up this very convenient card, however, is what at first appears to be the mundane problem of supplying to the card the small amount of power needed to drive the microprocessor and the memory.
The simplest approach would seem to be that of ordinary conduction. Metal contacts on the card would engage mating spring loaded contacts in the card reader, the machine that interfaces with the card, in a manner similar to that in which replaceable printed circuit boards are plugged into electronic equipment. The thousands of transactions daily that can occur with a busy reader, however, can create a very serious wear problem. Potentially even more important than the wear problem, however, is that of non-conductive dirt. Not only can the card contacts easily accumulate dirt and grit that would make the contact unreliable, but it has become an all too common prank for vandals to spray aerosol, non-conductive paint directly into the receptacles of publicly accessed machines.
Batteries are in general too bulky to be carried in a normal sized plastic card, even modern watch batteries. Solar cells can be made to work, but high light levels would have to be provided inside the reader, and considerable card space used.
While capacitive information transfer is practical, experience has shown that for capacitive power transfer from the reader, large areas of the card would be used up, and the spacing between the capacitive plating on the card and that on the reader would have to be held to a closer tolerance than is practical. Variations of one or two-thousandths of an inch can create very high or very low voltages.
Finally, for inductive power transfer an air core transformer is insufficient; a magnetic core must be carried on the card. However, the normal flexing of a plastic credit card, such as occurs to one carried in a hip pocket, immediately destroys the magnetic properties of the core, disabling the power transformer. Until my invention, therefore, the lack of a satisfactory power transfer method has delayed the widespread use of a contactless "smart" personal data card.